This invention relates to spatial light modulators, and more particularly to a digital micro mirror device.
Spatial light modulators (SLMs) have found numerous applications in the areas of optical information processing, projection displays, video and graphics monitors, televisions, and electrophotographic printing. SLMs are devices that modulate incident light in a spatial pattern to form an image corresponding to an electrical or optical input. The incident light may be modulated in phase, intensity, polarization, or direction.
An SLM is typically comprised of an area or linear array of addressable picture elements (pixels). Source pixel data is first processed by an associated control circuit, then loaded into the pixel array, one frame at a time.
One type of SLM is the digital micro mirror device (DMD)(trademark) developed by Texas Instruments Incorporated. The DMD is a monolithic single chip circuit, having a high density array of 16 micron square moveable micromirrors on 17 micron centers. These mirrors are fabricated over address circuitry which has SRAM cells and address electrodes. Each mirror forms one pixel and is bistable, such that light directed upon the mirror will be reflected in one of two directions. For display applications, in an xe2x80x9conxe2x80x9d mirror position, light is reflected to a projector lens and focused on a display screen. In the xe2x80x9coffxe2x80x9d position, light is deflected to a light absorber. The array of xe2x80x9conxe2x80x9d and xe2x80x9coffxe2x80x9d pixels produces an image.
More detailed discussions of the DMD device and its use may be found in the following patents: U.S. Pat. No. 5,061,049; U.S. Pat. No. 5,079,544; U.S. Pat. No. 5,105,369; and U.S. Pat. No. 5,278,652. Each of these patents is assigned to Texas Instruments Incorporated.
The evolution and design variations of the DMD can be appreciated through a reading of several patents, also assigned to Texas Instruments Incorporated.
The xe2x80x9cfirst generationxe2x80x9d of DMD spatial light modulators implemented a deflectable mirror/beam. An electrostatic force was created between the mirror and the underlying address electrode to induce deflection of the mirror. The mirror was supported by torsion hinges and axially rotated one of two directions. In the bistable mode, the mirror tips land upon a landing pad. The following patents describe this first generation of DMDs: U.S. Pat. No. 4,662,746; U.S. Pat. No. 4,710,732; 4,956,619; and U.S. Pat. NO. 5,172,262.
The xe2x80x9csecond generationxe2x80x9d DMD has a mirror that is elevated above a yoke. The yoke is suspended over the addressing circuitry by torsion hinges. An electrostatic force is generated between the elevated mirror and an elevated electrode. The mirror and the yoke rotate, but it is the yoke that comes into contact with a landing electrode. The following patents describe this second generation of DMDs: U.S. Pat. No. 5,083,857; U.S. Pat. No. 5,600,383; and U.S. Pat. No. 5,535,047.
One aspect of the invention is a DMD type spatial light modulator fabricated on a substrate. The substrate contains memory and control circuitry for addressing the pixels of the DMD. Each pixel has addressing circuitry comprising a first portion that is proximate the substrate and a second portion elevated above the substrate. In one embodiment, the first portion of the addressing circuitry has electrodes on a metallization layer, and the second portion has electrodes at an elevated yoke layer. A yoke is supported over the addressing circuitry first portion. At least one hinge is connected to the yoke and supports the yoke. The hinge permits tilting of the yoke in response to electrostatic addressing. A mirror is elevated above and supported by the yoke, and is mirror positioned over the elevated addressing circuitry second portion.
At each leading edge of the yoke, a pair of springtips are operable to land on the addressing circuitry first portion. The spacing between the springtips of each springtip pair, the length of the springtips, and the height of the yoke are increased for xe2x80x9coptimal performancexe2x80x9d. This optimal performance provides greater clearance between the addressing circuitry first portion and the leading edge of the yoke without significant comprise to the electrostatic performance.
As explained in further detail below, one advantage of the invention is that it reduces the likelihood of shorting between the yoke and the underlying metallization layer when the mirror is fully landed on the metallization layer. Additional features of the pixel improve the contrast ratio of images generated by the DMD mirror array.